Unified Modeling Language (UML) has emerged as the software industry’s dominant modeling language. It is the de facto modeling language standard for specifying, visualizing, constructing, and documenting the components of software systems. Despite its prominence and status as the standard modeling language, UML has its critics. Opponents argue that it is complex and difficult to learn. Some question the rationale of having nine diagramming techniques in UML and the raison d’être of those nine techniques in UML. Others point out that UML lacks a comprehensive methodology to guide its users, which makes the language even more convoluted. A few studies on UML can be found in the literature. However, no study exists to provide a quantitative measure of UML complexity or to compare UML with other object-oriented techniques. In this research, we evaluate the complexity of UML using complexity metrics. The objective is to provide a reliable and accurate quantitative measure of UML complexity. A comparison of the complexity metrical values of UML with other object-oriented techniques was also carried out. Our findings suggest that each diagram in UML is not distinctly more complex than techniques in other modeling methods. But as a whole, UML is very complex–2-11 times more complex than other modeling methods.